1. Field of the Invention
Numerous methods are presently known for the disinfecting of water and aqueous solutions, as well as for the production of potable water. The purely physical purification of water in clarifying installations, wherein the water is generally filtered through different sand layers and, eventually, is additionally treated with activated charcoal, is primarily adapted for a large scale water supply. However, water can also purified and disinfected through ultraviolet radiation, through ozonizing, through chlorination or in an oligo-dynamic manner to such an extent as to be, without hesitation, usable as potable water.
The oligo-dynamic principle is essentially predicated on the ability of the smallest quantities of suitable metals and metal salts to deaden or to inhibit the propagation of lower organisms in aqueous or gelatinuous milieus.
Based on this principle, different processes and means have been developed for the disinfection of water, which are widely employed, for example, for swimming pools, potable water supply in railroad cars, camping locations, ships, for traveling and the like.
All of these known methods facilitate the production of a satisfactory potable water and its storage over a limited period ranging between a few hours and a few weeks. The potable water canisters obtainable in one-liter plastic containers as an emergency drinking water supply from the water works of the City of Zurich, even guarantee a satisfactory condition of the contents for six months up to one year. In contrast therewith, a lengthier storage period for potable water is currently not known.
Accordingly, it is an object of the present invention to facilitate the storage of water and aqueous solutions; however, in particular, it is used to provide water which remains potable over a period of some years.
A number of disinfection systems which employ metals having microbicidal effects are currently known. For example, U.S. Pat. No. 4,043,932 teaches the use of a highly soluble silver salt, such as silver nitrate complexed with chlorine wherein the sterilizing effect is achieved by the combined action of the metal and chlorine atoms. The complex so formed is claimed to have both a long term and short term sterilizing effect. U.S. Pat. No. 4,145,291 describes an apparatus for disinfection of drinking water which is made of a porous ceramic material having metallic silver incorporated in it. British Pat. No. 1,429,318 describes a method for preparing a sterilizing product which comprises molding powdered silver chloride having an excess of chloride ion, heating to drive off any excess chlorine, and using the formed silver chloride plate to provide a constant, slow-release source of sterilization. However, none of the known methods have described a method by which a metal alone can be used to provide both an immediate source of disinfection, coupled with a prolonged-release source of disinfection, yielding an effective, but simple long-term method of water sterilization.
The foregoing and other objects are achieved by means of the novel formed members which achieve the disinfection with a difficultly soluble metal salt having a solubility of a maximum of 100 mg/liter, which is shaped into a form in which it will not deteriorate in the aqueous environment. In contrast with the known processes, by means of which there is achieved only a rapid disinfecting action, or which require more than one source of disinfection, the present invention provides both a short term and a long term action, by giving an initial burst of effective concentration of metal ions which is achieved quite rapidly in accordance with the solubility product of the salt, and thereafter remains constant up to the complete dissolution of the metal compound.
It is an object of the present invention to provide a process for the production of a shaped product for a protracted active-material release, wherein the members will not decompose in the aqueous environment, said process comprising shaping, by deformation at a pressure of at least 8000 kg/cm.sup.2, at least one difficultly soluble metal compound having microbicidal activity into shaped form, and treating the compound in a manner which produces an outer metal oxide layer on the surface of the shaped product, said oxide layer being readily soluble in water, wherein the readily soluble metal layer of the shaped product provides an initial source of microbicidal activity, and the difficultly soluble metal compound provides a prolonged release source of microbicidal activity. The present invention also relates to the product so produced.
The following description primarily discusses the utilization of silver compounds. However, although such compounds are preferred for certain areas of application, other metal compounds which are difficult to dissolve, such as copper, tin or quicksilver compounds can also be utilized.
The utilization of a metal compound which is difficult to dissolve, for example, a difficultly soluble silver compound, such as silver chloride, AgCl, silver bromide AgBr, silver phosphate Ag.sub.3 PO.sub.4, silver oxide/silver hydroxide, silver carbonate Ag.sub.2 CO.sub.3, and so forth, allows a prolonged-release constant source of an active silver ion concentration which is necessary and sufficient for the disinfection of pure water or predetermined aqueous solutions. However, at the same time in order to initially rapidly and effectively kill all bacteria which are already present in the water or aqueous solutions, the difficultly soluble shaped metal product is also "activated" to render a portion of the shaped product readily soluble in water. Thus, the difficulty soluble metal is treated in such a way that a portion of the total product has a silver ion concentration which is higher by about a ten-potential in comparison with pure silver halogenide. In one embodiment, the "activation" can be carried out through the admixing of a more readily soluble silver salt, for example, silver phosphate, silver carbonate or silver hydroxide in an amend of about 1 to 10% relative to the silver chloride or bromide.
In a preferred embodiment, the activation is carried out through a thermal or chemical treatment, particularly in tablet form, for instance, through a short, and in general, a maximum 10 second long heating of the surface to high temperatures, preferably to about 1000.degree. C., for example, with hot gases, through acid treatment, and so forth. Produced hereby on the surface of the formed member is, at least partially, a silver oxide/silver hydroxide layer, which evidences a higher solubility product than the difficultly soluble metal.
In the present description, silver hydroxide and silver oxide are to be considered as being identical, inasmuch as silver hydroxide, as is known, is subject to an aging process which, upon the separation of water, leads from hydroxide to oxide.
The "activation" thus provides the sufficiently high initial silver ion concentration which is necessary in order to effectively initially destroy any bacteria already present in the water to be treated, while the remaining, source of disinfection once the initial disinfection is accomplished.
In the following Table I there are compiled the solubility products and the silver content of an equilibrated aqueous solution in milligrams/liter for a few silver compounds which are difficult to dissolve:
TABLE I ______________________________________ Silver content of an equilibriated Solubility solution in Compound Formula Product mg/liter ______________________________________ (a) Silverchloride AgCl 1,7 .times. 10.sup.-10 1,408 (b) Silverbromide AgBr 3,3 .times. 10.sup.-13 6,204 .times. 10.sup.-2 (c) Silvercarbonate AgCO.sub.3 8,2 .times. 10.sup.-12 21,8 (d) Silverhydroxide AgOH .sup. 2 .times. 10.sup.-8 15,2 (e) Silverphosphate Ag.sub.3 PO.sub.4 3,4 .times. 10.sup.-14 46,4 ______________________________________
While the compounds (a) and( b), and particularly the compound (a), due to their difficult solubilities, are best suited for the exceptionally long-term treatment of potable water, the compounds (c), (d) and (e) are excellent for spotting, in effect, for activation of (a) or (b). When used alone, however, (c), (d) and (e) are not quite safe for potable water due to their higher solubility, but are well suited for different other applications.
The silver compound or other suitable metal compounds which are difficult to dissolve, are in actual practice, most conveniently utilized in a form of an activated tablet or shaped product. The essence of such a tablet consists of in that metal ions in the same measure, as these would form a solid bond with microorganisms in an aqueous solution, will in accordance with the solubility product again go into solution from the tablet. This affords, at sealed conditions, a timewise practically unlimited retainability (in effect, the disinfection) of water or aqueous solutions even upon repeated recontamination.
That type of drinking or potable water, for example, which has been treated with silver chloride, on the basis of the silver ion concentration, is considered to be safe from a health standpoint. With respect to considerations of taste, it remains unchanged after a number of years. Furthermore, no discoloration of the water can be detected, and its bacteriological composition is satisfactory.
The shaped products, for example such as tablets, can be produced wherein the desired quantity of one or more silver compounds which are difficult to dissolve are pressed at a pressure of at least 8000 kg/cm.sup.2 up to 15 tons/cm.sup.2 into shapes of the desired form and size, for example into tablets, cubes, pearls, rods, and the like. Other useful shapes will be readily apparent to one skilled in the art. Generally, in the utilization of silver chloride or silver bromide, the above-mentioned "activation" is necessary to achieve the desired effect.
In the utilization of silver carbonate, silver oxide/silver hydroxide, silver phosphate in themselves, the tablets are advantageously brazed into an ion-permeable plastic material membrane, for example, Metricel VF-6" produced by the company Gelman, having a pore size of 0.45, since they can decompose under an intensive mechanical load (for example, ultrasound) or in the warmth in the water.
The inventive formed members are, above, all adapted to
(1) preservation of potable water (civil defense, war supply, military, in tropical countries, nourishing of infants),
(2) the disinfection of drinking water for domestic animals,
(3) air conditioning installations for the disinfection of the supplied water,
(4) in hospitals (breathing-air humidifiers and other medical apparatuses employing water, saline solutions, and others), and
(5) Generally, wherein it is necessary to provide for the disinfection of water or of predetermined aqueous solutions.
It is recommended that water treated with the inventive formed members be stored in containers constituted of plastic material, ceramic glass or nobler metals such as silver, or in containers clad with such materials, in order to not disturb the oligo-dynamic action of the silver ions through a reaction with baser metals.
The minimum required concentration of silver ions in water, which is usually necessary and sufficient for the long-term disinfection thereof, consists of 0.1 to 1.0 mg/liter. Contrastingly, for the rapid and effective disinfection, in particular for an expected massive recontamination, there are, however, indicated initial silver ion concentrations of up to about 5 mg/liter. In general, the silver compounds are utilized in such a quantity that the active material concentration consists of at most 10 mg/liter.
Generally, the dosage consists of 200 mg of a difficultly soluble silver compound for 10 to 60 liters of water, regulated in accordance with the desired duration for maintaining the sterility.